The pressure sensors according to the invention are used, for example, for pressure measuring in internal combustion engines. The work room of the internal combustion engine would be in this case the pressure measuring space. The invention, however, is in no way restricted to this particular case of application.
If the pressure of the internal combustion process is known it is possible to optimise the combustion process accordingly, and, in particular, to use the used energy sources more efficiently.
The pressure wave occurring during the combustion process is accompanied by a temperature wave because of the combustion process going off like an explosion. Here this temperature shock wave together with the pressure wave hits the sensor, that means in particular the membrane of the sensor. The membrane has a suitable measuring device for measuring its pressure dependent deformation, and to define the accordingly connected pressure.
Now the membrane does not only experience mechanic stress because of the pressure wave, but it is also stressed mechanically because of the temperature shock wave. Because of the temperature-dependent length extension the membrane is deformed also mechanically only because of the temperature level and leads to a measurement error as the effect is not pressure-dependent.
Usually the sensor is built in near the pressure measuring space, for example in the motor unit which is well cooled by cooling water. Therefore also the sensor is generally thermally well connected with the motor unit and therefore also cooled well.
The sensors kept at normal operation temperatures, for example 80° C., experiences then in periodic cycles, according to the combustion process, a thermal peak stress of several hundred degrees at the membrane. This leads to a large temperature gradient in the membrane carrier, and, in particular, in the membrane with the risk that the different wire strain gauges forming the measuring device and connected according to a Wheatstone bridge circuit to each other have a different temperature level, and therefore also can contribute to considerable measuring errors.